Nitrogen cycle - kau

Nitrogen cycle

The nitrogen cycle is the biogeochemical cycle that describes the transformations of nitrogen and nitrogen-containing compounds in nature.

The basics

Earth's atmosphere is about 78% nitrogen making it the largest pool of nitrogen

Nitrogen is essential for many biological processes; it is in all amino acids, is incorporated into proteins, and is present in the bases that make up nucleic acids, such as DNA and RNA

In plants, much of the nitrogen is used in chlorophyll molecules which are essential for photosynthesis and further growt.

Processing, or fixation, is necessary to convert gaseous nitrogen into forms usable by living organisms.

Some fixation occurs in lightning strikes, but most fixation is done by free-living or symbiotic bacteria.

These bacteria have the nitrogenase enzyme that combines gaseous nitrogen with hydrogen to produce ammonia

Schematic representation of the Nitrogen cycle

Characteristics of the cycle

95 % of dissolved nitrogen is in the form of molecular nitrogen N2

Nitrogen has 9 oxidation states from -3 to +5

+5

NO3-, N2O5

+4

NO2

+3

HONO, NO2-, N2O3

+2

NO

+1

HONNOH, HO2N2-, N2O22-, N2O

0

N2

-1

H2NOH, HN3, N3-

-2

H2NNH2

-3

RNH2, NH3, NH4+

Presence of internal processes such as , nitrogen fixation,

nitrification and denitrification

Unbalanced budget

At the pH and pE of seawater all the nitrogen should be present as NO3-

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